In a related art, there is a well-known resistance-change type sensor that detects a change in resistance of a sensor element by a predetermined environmental change to measure a physical property of a target. A pressure sensor in which a so-called piezoresistance effect is utilized may be cited as an example of the resistance-change type sensor. In the piezoresistance effect, a resistance value is changed when a stress is applied to a physical body. The pressure sensor is widely used in various fields, for example, an in-car electronic device such as a sheet sensor and a consumer electronic device such as a blood pressure meter. Specifically, in this kind of resistance-change type sensor, as depicted in FIG. 21, a resistance value of a sensor element Rs is changed when an environmental change such as a stress is fed. A change in resistance ΔRS of the sensor element Rs is converted into a voltage by a current IO supplied from a current source 1, and an amplifier 2 amplifies the converted minute voltage ΔVs(=ΔRs×IO). The amplified output voltage VOUT (see the following equation) is supplied as a signal proportional to the environmental change to a subsequent-stage system (not depicted).VOUT=G×ΔVs=G×ΔRs×IO
where G is a gain of the amplifier 2. A rate of change of the change in resistance ΔRs with respect to the environmental change fluctuates according to a temperature. That is, the change in resistance ΔRs of the sensor element Rs has a predetermined temperature characteristic α. When the change in resistance ΔRs has the temperature characteristic α, the output voltage VOUT fluctuates according to the temperature characteristic α.VOUT=G×ΔRs×α×IO
Therefore, even in the same environmental change (for example, the same pressure change), the output voltage VOUT varies depending on an ambient temperature at that time. This causes an error.
For example, as disclosed in Japanese Patent Publication Laid-Open Nos. 03-200381 and 2007-097056, the temperature characteristic of the current IO supplied to the sensor element Rs is set to 1/α such that the temperature characteristic α of the change in resistance ΔRs is compensated, which allows production of the output voltage VOUT independent of the temperature characteristic α as follows.VOUT=G×ΔRs×α×IO/α=G×ΔRs×IO
The current having a temperature characteristic that compensates a signal gradient with respect to a signal having a temperature characteristic changed at a predetermined gradient to the temperature change is produced. Specifically, outputs of a plurality of constant current sources having different temperature characteristics are combined to change a gradient of the temperature characteristic of the constant current source, thereby producing the current having the desired gradient. Thus, in the circuits disclosed in Japanese Patent Publication Laid-Open Nos. 03-200381 and 2007-097056, when the temperature characteristic has the gradient that is linearly changed with respect to the temperature change, the temperature characteristic may be compensated (corrected). However, the temperature characteristic of the signal of the correction target may not simply increase or decrease, but sometimes the temperature characteristic is changed in a curved line with respect to the temperature change. For example, in the pressure sensor in which the piezoresistance effect is utilized, as depicted in FIG. 22, the change in resistance ΔRS of the sensor element Rs has the temperature characteristic α in which a high temperature side and a low temperature side of a predetermined temperature Ts differ from each other in the gradient due to an influence of a surface impurity concentration of the sensor element. Even in such cases, the circuits disclosed in Japanese Patent Laid-Open Nos. H03-200381 and 2007-097056 produce only the current having a temperature characteristic β (see alternate long and short dash line of FIG. 22) of the gradient linearly changed with respect to the temperature change. Therefore, a range on the low temperature side of a predetermined temperature T1 where the temperature characteristic α may not be compensated (corrected) is generated even if the gradient of the temperature characteristic β is freely adjusted. In the temperature range, because the influence of the temperature characteristic a may not be removed, the temperature characteristic α of the resistance-change type sensor becomes an error which causes detection accuracy to be lowered. Accordingly, in the complicated temperature characteristic in which the high temperature side and low temperature side of the predetermined temperature differ from each other in the gradient of signal change, it is preferable to produce the current whose temperature characteristic may be corrected with high accuracy.
The resistance-change type sensor is described above only by way of example. A similar problem is generated when the signal of the correction target has an unintended temperature characteristic.